JPS626587B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an epoxy resin molding material having excellent moldability. The purpose is to provide an epoxy resin molding material that has excellent moldability, electrical properties, and heat resistance. More specifically, when used as a molding material for encapsulating semiconductor devices, it can be molded into direct contact with the semiconductor element without requiring any special treatment on the surface of the semiconductor element, and has little effect on reliability, especially the rated value during semiconductor operation. The objective is to provide a material that has extremely good moldability. Furthermore, it is an object of the present invention to provide a material that has sufficiently low material viscosity during molding, has small burrs, and has a good molding cycle. When an epoxy resin molding material is used as a molding material for low-pressure semiconductor encapsulation, the molding method generally employed is a transfer molding method or a compression molding method. The semiconductor element is mounted in a frame shape, and since this is integrally molded as an insert product, lead wires usually protrude outside the mold cavity. A simple schematic diagram is shown in FIGS. 1 and 2. Second
In the cross-sectional view shown in the figure, the lead frame is sandwiched between the upper mold and the lower mold, thereby fixing the frame, and the heated and melted epoxy resin molding material fills the inside of the mold cavity and hardens by applying sufficient pressure. Ru. Semiconductor devices are sealed and molded in this manner, but in this case it is impossible to suppress variations in the clearance (gap) between the upper and lower molds and the frame thickness to within several μm. Therefore, the heated and melted epoxy resin flows into the gap between the lead frame and the upper and lower molds, forming flashes. When semiconductor products are used, these spilled burrs may cause the solder to be repelled and not stick, or may adhere to the mold during molding, impairing the product's release properties, or deforming or distorting the frame, which may adversely affect the semiconductor element. This becomes a big problem. In Fig. 1, the allowable length of the burr flowing out is normally within 1.5 mm from the cavity end face. The cause of the above-mentioned problem is that phase separation occurs between the filler used in the epoxy resin molding material and the resin or curing agent, and only the resin system (including the curing agent) seeps out due to its low viscosity. Alternatively, the surface wetting of the filler and resin system is poor, resulting in turbulent flow within the cavity, deforming the frame during flow and seeping out, or local variations in the thickness of the frame. Among the causes mentioned above, variations in the frame can be solved by controlling the thickness tolerance, but in the case of materials, most of the fillers used are inorganic and inherently have poor wettability with the resin, so this problem can be solved. It was very difficult to do so. Normally, epoxy resin molding materials are manufactured by pulverizing and mixing resin, curing agent, curing aid, filler, mold release agent, coloring agent, etc., and then kneading this mixed powder with a kneading machine such as a roll, kneader, or extruder while applying heat. However, in this state, it is impossible to melt and disperse the resin system and filler until they are completely wet. The reason for this is that since the curing agent and resin are kneaded at the same time, curing progresses and gelation occurs before the filler and resin get wet.On the other hand, if the temperature is lowered to suppress the acceleration of gelation, the kneading effect will be sufficient. This is so that you will not be affected. The present invention has been made in view of the above points, and its purpose is to improve moldability, especially burr-free properties, while maintaining the composition of an epoxy resin molding material for semiconductor device encapsulation, which has a proven track record of reliability. The goal is to improve liquidity. The present invention is characterized in that, as a method for improving burrs and fluidity of an epoxy resin molding material, the entire amount or a portion of the filler is melt-mixed with a pre-molten epoxy resin or a hardening agent, and the mixture is used. do. The melting temperature of the epoxy resin or hardener used and the filler must be at least 10°C higher than the softening point or melting point of the resin or hardener; below this, wetting effects with the filler cannot be expected. . Therefore, the effects of the present invention cannot be achieved even if the mixture is kneaded with a hot roll or the like at a temperature lower than this. The melt mixing time is preferably 20 minutes or more, although it depends on the mixing efficiency.The criterion for this judgment is to measure the minimum viscosity using a viscometer, and the process is completed when this becomes stable. Melt mixing can be carried out in any pot, beaker, kneader, etc. as long as it can heat and mix or stir. The epoxy resin applicable to the present invention refers to all known epoxy resins, such as bisphenol epoxy resins, novolac epoxy resins, and epoxy resins obtained from alicyclic compounds such as cyclohexene and cyclobentadiene. There are resins, etc., and at least one of these is used. As the curing agent, anhydrous acids such as tetrahydrophthalic anhydride, phthalic anhydride, etc. or phenol novolac resins are used. Examples of the filler include inorganic fillers such as silica, quartz glass, zirconium silicate, alumina glass fiber, talc, clay, and calcium carbonate, and these may be used in combination as necessary. When performing melt mixing, the decision whether to use an epoxy resin or a hardening agent is determined by the softening temperature of the material, and it is usually desirable to use the material with a lower softening temperature from the viewpoint of process and time. The amount of filler to be melt-mixed is preferably 50% by weight or more of the total amount of filler used in the epoxy resin composition. The epoxy resin or the molten mixture of the curing agent and filler thus obtained can be used in the same form as conventionally, and an epoxy resin molding material can be produced. Specific methods for kneading include methods using mixing rolls, co-kneaders, extruders, extruders, pressure kneaders, and the like. The present invention will be explained below according to examples, but the present invention is not limited in any way. In addition, parts in the following examples mean parts by weight. Example 1 (A) Softening point of cresol novolac type epoxy resin
73℃ (ring and ball method) (ECN1273 manufactured by Ciba) 100 parts (B) Phenol formaldehyde novolac resin (HP-607N manufactured by Hitachi Chemical) 55 parts (C) 2-heptadecylimidazole 2 parts (D) Carnauba wax 2 parts (E) 410 parts of silica powder The above composition was mixed uniformly, kneaded for about 8 minutes using a mixing roll preheated to 70 to 80°C, and then cooled to room temperature and pulverized to obtain an epoxy resin molding material. Obtained. On the other hand, the epoxy resin (A) and the filler (E) were heated to about 110° C. and melted and mixed for 20 minutes, taken out into a stainless steel vat, cooled, and then crushed. Add each material (B), (C), and (D) to this molten mixture and mix uniformly.
An epoxy resin composition [] was prepared using a mixing roll in the same manner as the epoxy resin composition []. Epoxy resin composition [] is the conventional manufacturing method, and [] is the method of the present invention. Table 1 shows the properties of the molding material obtained.

[Table] Example 2 (A) Phenol novolac type epoxy resin (XD-7855 manufactured by Dow) 100 parts (B) Tetrahydrophthalic anhydride (melting point 98°C (capillary method) (THPA manufactured by Shin Nihon Rika) 45 Part (C) 1 part of 2-methylimidazole (D) 2 parts of carnauba wax (E) 380 parts of quartz glass powder Heat the hardening agent (B) and filler (E) to about 100°C and melt and mix them for 30 minutes. , a molten mixture [] was obtained.For comparison, the amounts of filler (E) were 260 parts, 190 parts, and 190 parts, respectively.
Use 150 parts, hardening agent (B) and molten mixture [] []
[] was created in the same way as []. The obtained molten mixture [][][][] was kneaded in the same manner as in Example 1 using a mixing roll at 60 to 70°C for 10 minutes and cooled to obtain an epoxy resin composition.
From [] to [], the fluidity of the material was determined by spiral flow, and the curing property was determined by gel time and hardness. The conditions were 170°C, pressure 70Kg/cm ² for 20 minutes. The burr length shown in Table 1 is 100μm and 50μm for the mold, respectively.
Make grooves with depths of m, 30 μm, 20 μm, and 10 μm,
The length of the material seeping out was measured. From Table 1, the epoxy resin molding material according to the present invention [] has a fluidity (spiral flow) of about 30
% elongation and the clearance for burrs is 50 μm or less. When the burr is 100μm, it becomes large, similar to the spiral flow, but this means that sulfur flow often occurs even when the gap between the insert and the insert is very narrow, and the mold clearance cannot currently be increased by 100μm. It's not a problem at all because there isn't. The present invention provides not only moldability but also other effects. This is because the moisture resistance level of the cured epoxy resin molding material has been further improved. The decrease in volume resistivity after boiling is due to deterioration due to water penetration, but according to the method of the present invention, the volume resistivity increases by more than 1, which is due to improved wetting between the resin system and filler interface and stronger bonding. This is thought to be the result of Therefore, unmelted filler was added before kneading with a mixing roll so that the total amount of filler was 380 parts. The properties of the obtained epoxy resin molding material are shown in Table 2.

[Table] From Table 2, the epoxy resin molding material using about 40% molten mixture cannot keep the burr length below 1.5 mm and has poor solderability in actual molding. Furthermore, the moisture permeability level was about one order of magnitude lower than the other three epoxy resin compositions, indicating that no effect was achieved. In comparison, the molding material using a melt-mixed filler according to the present invention can suppress the burr length to 1.5 mm or less, as in Example 1, and has good solderability during mounting. It can also be seen that the moisture resistance level is further improved. Therefore, the epoxy resin molding material according to the present invention improves moisture resistance and moldability while maintaining the composition that has been proven in the past, so it can be used not only for transistors and diodes, but also for applications that are more complex and require higher reliability. This will further improve the reliability of encapsulation of LSIs, ICs, etc.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a general semiconductor package, and FIG. 2 is a sectional view of a molding die. Explanation of symbols, 1... Epoxy resin molding material, 2
...Lead frame, 3...Mold upper mold, 4...Mold lower mold, 5...Mold parting surface, 6...Mold cavity, 7...Semiconductor element.

Claims (1)

[Claims] 1. In a method for producing an epoxy resin molding material by mixing an epoxy resin, a hardening agent, a filler, and an additive, the filler and the epoxy resin or the hardening agent are mixed in advance at the softening point of the epoxy resin or the hardening agent. Alternatively, a method for producing an epoxy resin molding material, which comprises melting and mixing at a temperature 10°C or more higher than the melting point, pulverizing, and then mixing other components of the molding material. 2. The method for producing an epoxy resin molding material according to claim 1, wherein 50% by weight or more of the filler is melt-mixed with an epoxy resin or a hardening agent.